In order to provide navigational assistance (image-assisted surgery) during a medical procedure, such as a procedure involving the pelvis, the spatial position of the pelvis is ascertained. It is of particular interest to ascertain how specific anatomical pelvic planes lie in a space defined by a coordinate system of a medical tracking system (which may be assigned to a medical navigation system). Planes of interest include, for example, the frontal pelvic plane, which is defined by the two iliac spines and the two pubic spines, and/or the mid-sagittal pelvic plane.
EP 1 632 193 A1 describes a hip registration system comprising a registration frame provided with reflective markers. When using such a registration frame, a sufficient number of markers should be detected in a free line of sight by the tracking cameras of the tracking system.
US 2003/0153829 A1 discloses a navigation system for pelvic operations in which a patient positioning frame is used. A reference array is attached to the frame, wherein the frame, based on the reference array, can be registered using a pointer instrument.